[Noisebridge-discuss] charging a cap with a xtal?

[Johny Radio]

On 9/12/2013 10:38 AM, macegr wrote:
> Must you actually charge it with the oscillator, or are you simply 
> attempting to generate a time-dependent voltage on the capacitor?

must actually charge it with the crystal osc, because our challenge is 
to make something with the parts given us by Instructables.com.

> If you're using a TTL oscillator module, it might be outputting a 5V 
> square wave. This would allow you to charge a peak-detector circuit 
> (diode inline to capacitor connected to ground, optional drain 
> resistor) to within maybe 0.6V below VCC. This will be harder if 
> you're trying to connect directly to an oscillator circuit without an 
> output buffer.

ok, i can add a transistor buffer to the xtal output if necessary. I'm 
assuming the resistor will determine the charge time of the cap. Is this 
correct:

                                                 OSC--
                                                          |
                                                          |
                                                       Diode
                                                          |
                                                          |
                                                       Capacitor
                                                          |
                                                          |
                                                       Resistor
                                                          |
                                                          |
                                                        GND


Johny Radio


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.noisebridge.net/pipermail/noisebridge-discuss/attachments/20130912/adfe91df/attachment.html>